This strange device makes underwater objects invisible to sonar.

A team of researchers at the University of Pennsylvania, led by Amanda D. Hanford, has developed an underwater cloaking device based on a protective metamaterial capable of intercepting and “warping” sound waves emitted by sonar. As a result, the waves are scattered, and the "effect of absence" of a real object is created.

Metamaterials have properties that are not found in nature. They are usually made from composite materials - metals, plastics, or ceramics - combined into repeating microscopic structures.

The Hanford team's goal is to create a metamaterial that will hide underwater objects and, above all, submarines from detection equipment. Previously, it was possible to simulate the cloaking effect only in the laboratory, and only in the air.

As conceived by Handford and her colleagues, the protective "cloak" was to consist of metamaterial, the cells of which are less than the length of the sound wave. As a result, an experimental prototype was created in the form of a pyramid of perforated steel plates 91 cm high.It was placed in a large laboratory tank filled with water, where a hydrophone was also installed, generating sound waves with a frequency of 7000 to 12000 Hz and several receiving hydrophones for recording echoes. signals.

The researchers found that sound waves are reflected from the protective material in such a way that the object inside becomes invisible.